molecular cloud

History

In the mid-20th century, astronomers assumed that interstellar matter accumulates in dense clumps that give birth to stars. In the 1970s, radio observations of carbon monoxide (CO) for the first time directly detected giant molecular clouds in our Galaxy.

How it works

Gravity slowly pulls the cloud's matter inward. If enough mass accumulates in some region, gravity overcomes the internal pressure, and the clump begins to contract faster and faster. In the end, at its center, the temperature becomes so high that nuclear reactions ignite—a star is born.

History

In the mid-20th century, astronomers assumed that interstellar matter accumulates in dense clumps that give birth to stars. In the 1970s, radio observations of carbon monoxide (CO) for the first time directly detected giant molecular clouds in our Galaxy.

How it works

Gravity slowly pulls the cloud's matter inward. If enough mass accumulates in some region, gravity overcomes the internal pressure, and the clump begins to contract faster and faster. In the end, at its center, the temperature becomes so high that nuclear reactions ignite—a star is born.

History

The first indication of the existence of molecules in the interstellar medium: detection of CH and CN in optical spectra (1937). In 1970, with the discovery of CO emission at a wavelength of 2.6 mm, systematic mapping of molecular clouds began. In 1975, Fred Hoyle and colleagues published a model of chemical evolution of clouds. Large surveys of the 1980s–2000s (FCRAO, Bell Labs 7-m) revealed thousands of clouds in the Milky Way. Modern interferometers (ALMA) with high resolution showed a complex filamentary structure and disks around protostars.

How it works

Dynamics are controlled by the balance of gravity, thermal pressure, magnetic field, and turbulence. Stability is determined by the Jeans criterion: if the mass of a gas clump is greater than the Jeans mass M_J ∝ T^{3/2} ρ^{-1/2}, it collapses. Compression accelerates, the cloud fragments into many clumps—a star cluster forms. During compression, gravitational energy is released, part of it turns into heat, part into magnetic field energy and kinetic energy of outflows. When the temperature in the center of the protostar reaches ~10⁷ K, nuclear burning of hydrogen begins. The newborn stars ionize the surrounding gas (creating H II regions) and through stellar wind and radiation disperse the remnants of the cloud.

Open problems & fun facts

How exactly collapse is initiated: the role of turbulence and shock waves from supernovae.; The origin of complex organic molecules in cold prestellar cores (prestellar chemistry).; Detection of protostellar disks at the earliest stages and connection with planet formation.

💡 In the Sagittarius B2 cloud, ethyl formate has been found—the substance that gives raspberries their aroma; so in some regions, space literally 'smells' of berries.